Climate Change Is Not So Hot for Great Lakes Fish and Fishermen
It doesn’t have the same drama as the rising sea swallowing an Alaskan village, but warmer temperatures in the Great Lakes could have huge implications for lake fish, the people who catch them, and the dinner plates they end up on.
“We’re turning up the thermostat, but that completely reconfigures the entire food web, including the chemistry that’s going on within the lake,” said Paul Venturelli, assistant professor in the department of fisheries, wildlife, and conservation biology at the University of Minnesota. “That reverberates all through the food web, essentially from the bottom up to the top.”
Climate change is expected to increase surface temperatures of the Great Lakes by as much as 7 degrees Fahrenheit, and the working theory has for some time been that warmer temperatures mean rapidly growing fish. That sounds like a good thing, and in some cases, it is. Salmon-family whitefish, the most economically valuable commercial fish in the upper Great Lakes, are projected to benefit from higher temperatures. Nearly 10 million pounds of whitefish—which Fannie Farmer called the finest Great Lakes fish—are caught in the region annually. Projections say lake trout stock will also remain stable or increase.
“The assumption there is they can still get the same food that they got before,” Venturelli said. But when the food web rearranges itself as the result of the changing temperatures, that the same food will still be available is a big assumption. And the problems that can create are already affecting a local fish-fry favorite, walleye.
In August, Minnesota’s Department of Natural Resources placed an unprecedented ban on walleye fishing in Mille Lacs Lake. Venturelli said warmer temperatures and increased water clarity were two factors negatively impacting the fish, leaving walleye with less food to eat. The governor suggested restocking the lake with more walleye. “I kind of liken it to picking up a hammer when you need a saw,” Venturelli told a local news station. “It makes no sense.”
The issue of fish food also came up again this summer in a new study from Ohio State University, which found that yellow perch, whose stocks in Lake Erie have been low since 2003, aren’t adapting well to warmer, earlier springs. Both yellow perch and walleye need prolonged periods of temperatures below 10 degrees Celsius to reproduce well. Otherwise, they produce smaller eggs and less robust larvae. These larvae might be able to survive, but yellow perch live by the same principle as love—timing is everything.
In both the lab and the field, researchers observed that female walleye continued to spawn in the historically atypical months of April and May, and even when air temperatures reached the 80s in March in 2012.
“In lots of cold-blooded species, we find that as spring occurs earlier, the timing of reproduction will also move forward,” said Stuart Ludsin, principal investigator of the study and an associate professor of evolution, ecology, and organismal biology at OSU. “Walleye are a great example. In the record short winter of 2012, walleye moved their spawning period up by several weeks. With yellow perch, we didn’t see that.”
But the supply of zooplankton that yellow perch larvae eat will have already peaked with the early arrival of warm weather. If food is scarce at the time eggs hatch, larvae will grow slowly and remain vulnerable to invasive white perch, a key predator in Lake Erie.
“There’s this mismatch that occurs between the larvae and the food. It flies in the face of the general assumption that warmer, shorter winters are good,” Venturelli said. “We tend to think of winter in human terms. It’s something we need to put up with. For fish it’s different. They actually need it.”
And they’re on the move to get it, with fish that prefer colder temperatures moving north and to deeper parts of the lakes as surface temperatures get too warm for them. Venturelli said this could have huge implications for the $7 billion Great Lakes fishing industry.
“It’s going to favor those stakeholders in Ontario over those in the U.S. And so you have this shared resource, if walleye are distributed fairly evenly throughout the lake. But if they all move north of the border into Canada, suddenly you have haves and have nots,” he said.
“If we’re going to lose walleye it’s going to be in the Southern half of Lake Erie, that’s where you’d be hearing it first,” he added.
Estimates suggest that this won’t happen for another 50 to 100 years, but Lake Erie fishermen are dealing with other problems in the meantime. Bob Witt is a third-generation commercial fisherman with 33 years of experience on the lake. He owns Lake Erie’s Sea Breeze Charters, which runs trips for folks looking to hook their own walleye.
“Walleyes have always migrated around the lake. I don’t know that the warming has changed that,” he said. “Our big thing here is we’ve got algae in the lake in late summer. Heavy rains washed all the phosphorus out of the fields into the lake. That’s what we’ve been dealing with lately.” Sometimes the fish still bite when there’s a bloom, but other times they don’t, “and you think that’s what it is,” the algae, that keeps the walleye away, Witt said.
“I don’t think we did as much business because of the algae; our trips are way down because of it,” he added. Invasive species such as zebra mussels, Asian carp, and sea lampreys are also wreaking havoc.
Still, climbing aboard Witt’s boat is the best option if you want to eat local walleye. “Minnesota is kind of known for its walleye,” Venturelli said. “But if you’re eating walleye at a restaurant, it’s from Canada.”